Prevalence of intestinal parasite infections on a national scale among primary schoolchildren in Laos

In order to investigate the epidemiological situation of intestinal parasite infections in Laos, parasitological surveys were carried out on a national scale including 17 provinces and the Vientiane Municipality. A total of 29,846 stool specimens were collected from primary schoolchildren from May 2000 to June 2002 and examined once with the cellophane thick smear technique. The cumulative egg positive rate for intes-tinal helminths was 61.9%. By species, the rate for Ascaris lumbricoides was 34.9%, hookworm 19.1%, Trichuris trichiura 25.8%, Opisthorchis viverrini 10.9%, Taenia spp. 0.6% and Hymenolepis spp. 0.2%. The northern mountainous regions such as Phongsaly, Huaphan or Saysomboune Province showed a higher prevalence (over 70%) of soil- transmitted helminths. The regions along the Mekong River such as Khammuane, Saravane or Savannakhet Province showed a higher prevalence (over 20%) of fish-borne parasites. On the other hand, Schistosoma mansoni eggs were detected in 1.7% of schoolchildren only in Champassak Province, a previously endemic area. The highest prevalence was noted in Phongsaly Province (96.0%) and the lowest in Bolikhamxay Province (27.5%). An additional small-scale survey by cellophane anal swab detected Enterobius vermicularis eggs in 35.7% of 451 schoolchildren aged 6-8 years in Khammuane, Vientiane, Champassak Province and the Vientiane Municipality. Meanwhile, the mean blood haemoglobin level of hookworm-infected children was not lower than that of children not infected with hookworm, suggesting that nutritional factors are more important than parasite infection per se. Nevertheless, the above results indicate that a nationwide parasite control project is necessary to reduce possible morbidity due to parasitic diseases in the country.